Patients with Alzheimer's disease (AD) often develop insomnia, shifting of the major sleep period, or disturbed behavior at night. The identification of disrupted circadian rhythm in AD may lead to the intervention of this problem, in particular behavior or light therapy. The aims of this study are to determine if the circadian rhythm of four variables (rest, temperature, melatonin, cortisol) in pts with AD are abnormal; to discern any alteration of the relationship between two different circadian pacemakers (X and Y) in AD.